Contact lenses are a widely used and effective method for vision correction across the United Kingdom, but they are medical devices that interact directly with the sensitive ocular surface. While the lenses themselves are manufactured under stringent sterile conditions, their use can increase the risk of eye infections if specific hygiene and maintenance protocols are not strictly followed. Most complications arise when the natural protective barriers of the eye are compromised or when harmful microorganisms are introduced via contaminated lenses, cases, or water. Understanding these clinical risks and adhering to professional safety guidance is essential for maintaining long term ocular health and ensuring that contact lenses remain a comfortable part of daily life.
What We’ll Discuss in This Article
- The biological mechanisms that lead to contact lens related infections.
- Common types of infections, including microbial and Acanthamoeba keratitis.
- How improper handling and hygiene increase the likelihood of bacterial growth.
- The specific risks associated with tap water and contact lens care.
- Why sleeping in contact lenses significantly heightens the risk of complications.
- Clinical signs of infection that require immediate medical attention.
How Contact Lenses Interact with Eye Health
The surface of the eye, specifically the cornea, relies on a constant supply of oxygen and a healthy tear film to remain clear and infection free. When a contact lens is placed on the eye, it can act as a physical barrier that slightly reduces the amount of oxygen reaching the corneal surface. This can lead to minor swelling or microscopic breaks in the corneal epithelium, which are the outermost cells of the eye. These tiny breaks provide an entry point for bacteria and other pathogens that would normally be washed away by tears and blinking.
Furthermore, contact lenses can serve as a surface for biofilms to form. A biofilm is a thin, slimy layer of bacteria that adheres to the lens material, protecting the microbes from the eye’s natural immune defences and even some types of cleaning solutions. According to Moorfields Eye Hospital NHS Foundation Trust, while serious infections are relatively rare, the presence of a foreign object like a lens naturally alters the ocular environment, making it more susceptible to external pathogens if hygiene standards slip.
Understanding Microbial Keratitis
Microbial keratitis is the most common serious infection associated with contact lens wear. It occurs when bacteria, such as Pseudomonas aeruginosa or Staphylococcus aureus, infect the cornea. This condition can develop rapidly and, if left untreated, can lead to permanent scarring and vision loss. The risk of developing microbial keratitis is significantly higher for those who use reusable lenses compared to those who use daily disposables, primarily because of the increased handling and the potential for contamination within the lens case.
The risk is further amplified by the practice of extended wear or sleeping in contact lenses. When the eyelids are closed, oxygen levels at the eye surface drop even further, and the lens becomes a stagnant environment where bacteria can thrive. Clinical guidance from The College of Optometrists emphasizes that even lenses approved for overnight wear carry a higher infection risk than those removed before sleep. For most patients, a daily wear schedule where lenses are removed every night is the safest approach to prevent bacterial keratitis.
The Danger of Water and Acanthamoeba
One of the most devastating but preventable eye infections associated with contact lenses is Acanthamoeba keratitis. Acanthamoeba is a microscopic, single celled organism found commonly in tap water, swimming pools, hot tubs, and soil. While it is generally harmless to the skin, it can cause a severe and painful infection if it becomes trapped behind a contact lens. Because the organism can survive in the microscopic gaps of a lens or its storage case, it is vital that contact lenses never met water.
In the UK, awareness of no water protocols is a critical part of the contact lens fitting process. This means never rinsing lenses in tap water, never storing them in anything other than sterile solution, and always drying hands thoroughly before handling lenses. If you go swimming or use a hot tub while wearing lenses, the NHS recommends using tight fitting goggles and discarding the lenses immediately after getting out of the water to ensure no contaminants have been trapped against the cornea.
Lens Case Hygiene and Contamination
The contact lens case is often the weakest link in a patient’s hygiene routine. Many users diligently clean their lenses but neglect the case where they are stored. Over time, bacteria can build up inside the case, forming a layer that is difficult to remove. If the case is not rinsed with fresh solution and left to air dry upside down every day, it becomes a reservoir for infection. Using old solution, known as topping up, is particularly dangerous as it dilutes the disinfecting power of the liquid, allowing microbes to survive and multiply.
To minimise these risks, cases should be replaced at least every three months. For those who find the maintenance of reusable lenses challenging, daily disposable lenses are often recommended as a safer alternative. Because daily disposables are discarded after a single use, they eliminate the need for cases and solutions entirely, which significantly reduces the opportunities for environmental pathogens to reach the eye. Information from the General Optical Council highlights that consistent compliance with these simple steps is the most effective way to protect your sight.
Comparison of Infection Risk Factors
| Factor | Risk Level | Reason |
| Daily Disposable Lenses | Lowest | Fresh sterile pair every day; no storage required |
| Monthly Reusable Lenses | Moderate | Relies on user compliance with cleaning and case care |
| Sleeping in Lenses | High | Reduced oxygen and increased bacterial stagnation |
| Exposure to Tap Water | Very High | Potential for Acanthamoeba and other water borne pathogens |
| Extended Replacement | High | Build-up of protein deposits that harbour bacteria |
| Hand Washing (Soap & Water) | Reduces Risk | Removes transient bacteria before handling lenses |
Recognizing the Warning Signs
Early detection is the most important factor in successfully treating a contact lens related infection. The eyes have a limited ability to signal distress, so any unusual symptoms should be taken seriously. The primary indicators that something may be wrong include persistent redness, pain or a gritty sensation, blurred vision, and sensitivity to light. If you experience these symptoms, the first step is always to remove the contact lens immediately and do not attempt to reinsert it or try a new one.
If the symptoms do not improve quickly after removing the lens, or if the pain is severe, you should contact an optometrist or an eye casualty department immediately. Delaying treatment for a corneal infection can lead to complications that are much harder to manage later. Specialist eye hospitals like the Bristol Eye Hospital advice that patients should always have an up-to-date pair of glasses available so they can stop wearing their lenses at the first sign of irritation without compromising their ability to function.
Conclusion
Contact lens use can increase the risk of eye infections if proper hygiene and replacement schedules are not maintained. Bacterial and water borne pathogens can thrive on contaminated lenses or in poorly cleaned storage cases, potentially leading to serious conditions like microbial keratitis. However, by strictly following no water rules, removing lenses before sleep, and attending regular check-ups, the risk can be kept very low. If you experience severe, sudden, or worsening symptoms, call 999 immediately.
Why is tap water dangerous for contact lenses?
Tap water contains microorganisms like Acanthamoeba that can cause rare but devastating infections if they get trapped behind a contact lens.
Is it okay to sleep in my contact lenses just once?
Sleeping in lenses not designed for overnight use significantly increases infection risk due to reduced oxygen; it is best to remove them every night.
How often should I change my contact lens case?
You should replace your lens case at least every three months to prevent the build-up of bacterial biofilms.
Can I wash my contact lenses with saliva?
No, saliva is full of bacteria and should never be used to clean or lubricate a contact lens.
Are daily disposables safer than monthly lenses?
Daily disposables are generally considered safer because they eliminate the need for cleaning and storage, where many contamination issues occur.
What should I do if my eye is red after wearing lenses?
Remove the lens immediately and if the redness does not clear quickly or is painful, consult an optometrist or eye specialist.
Can a contact lens infection cause permanent blindness?
If left untreated, severe infections like microbial keratitis can cause corneal scarring that leads to permanent vision loss.
Authority Snapshot
This article provides a clinical overview of the infection risks associated with contact lens wear and the hygiene protocols required to mitigate them. It was reviewed by Dr. Rebecca Fernandez, a UK trained physician with extensive experience in emergency medicine and internal medicine. All guidance is strictly aligned with the standards set by the NHS, NICE, and the College of Optometrists to ensure patient safety and evidence-based education.
